The proposed effort aims to change the paradigm of medical diagnostics based upon antibody biomarkers, enabling diagnosis of hundreds of prevalent diseases and conditions using a single inexpensive test. Although antibodies presently serve as excellent biomarkers for several diseases, seldom are more than a few antibody specificities assessed in a single test. Furthermore, most current tests that measure antibody biomarkers typically do not provide sufficient diagnostic sensitivity and specificity when used alone. To address these problems, the specificities of a broad spectrum of the circulating antibody repertoire will be profiled simultaneously, using a novel integrated discovery and array construction process based upon living reagents. To demonstrate the intrinsic power and potential broad applicability of this approach, we will generate and clinically validate the utility of expandable antibody repertoire profiling microarrays for diagnosis, prognostication, and therapeutic monitoring of Celiac Disease. Using high-resolution antibody specificity data, novel self- and non-self antigens will be identified as the targets of serum antibodies that may be involved in disease onset or progression. Application of the antibody detection reagent discovery process to a large number of disease cohorts from multiple national centers will enable establishment of the human antibody specificity repertoire database, providing a broadly applicable tool to better understand disease etiology and personalize therapy for Celiac and other diseases. Success of this effort will reduce the cost of diagnostic tests and the economic burden of undiagnosed and misdiagnosed disease.